1. Field of the Invention
This invention relates to a motor assembly, more particularly to a brushless electric motor assembly having an axial tube for reliably positioning an antifriction bearing.
2. Description of the Related Art
Referring to FIG. 1, a motor structure disclosed in U.S. Pat. No. 6,882,074 B2 includes a stator 14 and a circuit board 13 which are engaged together and which are mounted to a hollow tube of a casing 11, and an axial tube 12 mounted into and in splined engagement with the hollow tube of a casing 11 from a bottom end of the hollow tube such that hook portions 122 of a plurality of resilient arms 121 are brought into engagement with the stator 14. A positioning ring 10, a supporting member 17, and an abrasion-resisting plate 20 are mounted into the axial tube 12. A sleeve 15 having a bearing 16 mounted therein is inserted into and is tightly engaged in the axial tube 12. A shaft 18 of a rotor 19 is extended through the bearing 16 and the positioning ring 10. Since the axial tube 12 and the sleeve 15 exert forces to each other, the sleeve 15 is tightly engaged with the bearing 16 and the resilient arms 121 are securely engaged with the stator 14.
However, such motor assembly has a large number of components, thereby resulting in inconvenience during fabrication and low assembling reliability. Moreover, with the opened-ended sleeve 15, lubricating oil between the bearing 16 and the shaft 18 may be squeezed out from the bottom of the sleeve 15 by the weight thereof so as to adversely affect running of the shaft 19 and make a noise.